Predicting borehole stability while drilling based on nonlinear inversion

The conventional borehole stability prediction methods are characterized by a large amount of calculation, complex operation and limited applicability, which can seriously affect real time application of the technology. Through intensive studies on the quantitative relationships between acoustic velocity, seismic data and borehole stability parameters, the direct seismic inversion model for pore pressure, in-situ stress and rock strength is established. Based on the nonlinear characteristics of the inversion model as well as the geological statistics features of borehole stability parameters, pore pressure, in-situ stress and rock strength of the formation to be drilled can be predicted by employing the stochastic inversion method so as to further forecast borehole stability. In actual drilling, the real-time geological logging data and layered statistical mode of borehole stability parameters can be used to predict borehole stability of the formation ahead of bit while drilling. The practical application of the proposed method in Yuanba Gas Field of Northeast Sichuan shows that the proposed method possesses strong ability of prediction while drilling and its comprehensive performance is significantly improved compared with the conventional methods.